The thermostat may be stuck open. There is another potential problem which is that the radiator fan(s) may be running all the time - I've just had this. On a cold start, the electric fan would run at full bore, and usually continue to do so, irrespective of engine temp. The cause turned out to be the temperature sender at the back of the block, by the bulkhead.
I only have an electric rad fan - depending on engine type, it seems some have two fans, diesels I believe, one being a viscous fan. If the car has a viscous fan, the coupling may have seized, so also worth a look see. If it is working properly, you should be able to stop it by gently (and carefully) holding a rolled up paper / cardboard to it.
Changing the sensor seems also to have fixed an irritating fault I'd never been able to track down (nor indeed could Audi). While cold, the throttle response wasn't all the smooth for the first mile or so - and when warm there was a minor flat spot, or "fluffing / hesitation" at just over 2,000 revs. The new sender seems to have fixed those too. I assume the ecu wasn't getting good data on temperature.
The car is a 53 plated 2.0 fsi. I believe our cars all have two temperature sensors - one at the bottom of the rad, the other (the main one) at the back of the block.